In commonly assigned U.S. Pat. Nos. 4,423,934, incorporated herein by reference, a photographic camera with a digital, microcomputer-based control system is described for controlling various camera operations. As described therein, such a camera is equipped with a number of transducers or sensors and user operated input switches which feed digitized input signals to the microcomputer at certain times representing the detection of events or conditions during the initiation of and through completion of an exposure. Such cameras are provided with scene light condition measuring sensors for providing scene light signals to the microcomputer for automatic exposure control. In addition, auto range finder sensors are provided for estimating the distance to an object in the scene aimed at by the user and for setting the lens focus accordingly, as are well known in the camera art. These and other condition sensors, switch inputs and digitally controlled camera operations are described in the '934 patent.
In addition, cameras are commonly provided with reversible motorized film advance mechanisms operated by the microcomputer based control system for advancing the filmstrip to the next image frame on completion of an exposure and for rewinding the entire filmstrip into its cartridge when all exposures are completed. Various types of metering systems are employed to control the frame advance to avoid overlapping frames or too wide a spacing between adjacent exposed image frames. In this process, filmstrip sprocket hole or perforation event detect opto-sensors are employed to detect the passage of the perforations as the filmstrip is advanced.
More recently, it has been proposed to provide a filmstrip having a magnetic layer on the non-emulsion side so that data may be recorded in or reproduced from tracks on the magnetic layer by magnetic heads in the camera and/or in photofinishing equipment. Commonly assigned U.S. Pat. No. 5,229,810, for example, discloses such a filmstrip having a magnetics-on-film (MOF) layer and a camera system utilizing the filmstrip. A variation on the filmstrip disclosed in the '810 patent is disclosed in my above-referenced '175 application. In such systems, it is necessary to provide a metering system for controlling particularly the recording of information in a track or tracks of the MOF layer during each frame advance while also controlling the metered distance the filmstrip is advanced. The metering system employs analog output signals generated by film perforation opto-sensors positioned in the filmstrip advance path in response to passage of one or more perforations past the sensor(s) during each frame advancement.
In all such systems, variances in system performance can result from variances in the sensor signal response to the measured variable and variances in the response of the electro-mechanical mechanism to a control signal from the microcomputer. In other words, the microcomputer can only perform the system operating algorithms it is programmed to perform, and system response is dependent on the accuracy of the sensor input signals and the responsiveness of the controlled mechanisms.
In the manufacture of such automatic, computer controlled cameras, it is desirable to be able to specify component performance, e.g. sensor performance, with as wide tolerance specifications as feasible, so that parts costs are kept reasonable. Such sensors can include the perforation sensors for filmstrip metering, the range finding sensor, a photovoltaic sensor or sensor array elements for auto exposure calculation in natural light or for controlling the decision to employ artificial (flash) illumination, and (optionally) for flash control feedback, and any other camera sensors that generally provide an analog output signal that must be digitized for use by the microcomputer in one of the camera system operations. For similar reasons, it is desirable to be able to specify rather loose tolerances of operating mechanisms, e.g. the aperture and blade mechanisms, the lens focus drive mechanism and the filmstrip advance mechanism.
As a result, performance in post-assembly tests of the affected camera systems can vary widely from camera to camera. As set forth in the above referenced '934 patent, as long as the particular camera system performance is within specification, the performance can be compensated for. Typically, such compensation involves adjustments to the sensor response at the output of the sensor, e.g. by trimming the response to one or more test conditions mimicking the condition or event to be detected to achieve either a target output signal level or the desired downstream target response by the controlled mechanism. Component trimming requires access to the camera circuits, is time consuming and costly, and results in some loss of product.
The manner of compensation proposed in the '934 patent is to operate the camera in a final camera assembly and quality control operation using a nominal parameter control program. The camera sensors and component mechanisms are exercised using a set of nominal control constants, and the system responses, i.e., the test output signal level or controlled operation response, are recorded. The errors from specified values are computed, and corresponding correction values are also computed. The digitized correction values are stored in memory in the camera microcomputer and are called up and employed to offset the digitized sensor output signal or to compensate for variations in settings achieved or operating times of the mechanisms during normal use of the system.
Problems to be Solved by the Invention
The '934 patent represents a significant improvement over the prior approach. However, it also involves the use of a test set-up and an external computing and programming operation that communicates data and commands between the computer and the camera. The camera must be in some state of disassembly for connections to be made to the camera circuitry.
The invention is directed to solving the above stated problems in the manufacture and testing of cameras and other equipment.